linux-kernel - Re: [PATCH 1/2] wan/hdlc_x25: make lapb params configurable

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Message-ID: <20200113055316.4e811276@cakuba>
Date:   Mon, 13 Jan 2020 05:53:16 -0800
From:   Jakub Kicinski <kubakici@...pl>
To:     Martin Schiller <ms@....tdt.de>
Cc:     khc@...waw.pl, davem@...emloft.net, linux-x25@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] wan/hdlc_x25: make lapb params configurable

On Mon, 13 Jan 2020 13:45:50 +0100, Martin Schiller wrote:
> This enables you to configure mode (DTE/DCE), Modulo, Window, T1, T2, N2 via
> sethdlc (which needs to be patched as well).
> 
> Signed-off-by: Martin Schiller <ms@....tdt.de>

> diff --git a/drivers/net/wan/hdlc_x25.c b/drivers/net/wan/hdlc_x25.c
> index 5643675ff724..b28051eba736 100644
> --- a/drivers/net/wan/hdlc_x25.c
> +++ b/drivers/net/wan/hdlc_x25.c
> @@ -21,8 +21,17 @@
>  #include <linux/skbuff.h>
>  #include <net/x25device.h>
>  
> +struct x25_state {
> +	x25_hdlc_proto settings;
> +};
> +
>  static int x25_ioctl(struct net_device *dev, struct ifreq *ifr);
>  
> +static inline struct x25_state* state(hdlc_device *hdlc)

Please no more static inlines in source files. Compiler will know what
to do.

> +{
> +	return (struct x25_state *)hdlc->state;
> +}
> +
>  /* These functions are callbacks called by LAPB layer */
>  
>  static void x25_connect_disconnect(struct net_device *dev, int reason, int code)

> @@ -186,6 +217,9 @@ static struct hdlc_proto proto = {
>  
>  static int x25_ioctl(struct net_device *dev, struct ifreq *ifr)
>  {
> +	x25_hdlc_proto __user *x25_s = ifr->ifr_settings.ifs_ifsu.x25;
> +	const size_t size = sizeof(x25_hdlc_proto);
> +	x25_hdlc_proto new_settings;
>  	hdlc_device *hdlc = dev_to_hdlc(dev);
>  	int result;
>  
> @@ -194,7 +228,13 @@ static int x25_ioctl(struct net_device *dev, struct ifreq *ifr)
>  		if (dev_to_hdlc(dev)->proto != &proto)
>  			return -EINVAL;
>  		ifr->ifr_settings.type = IF_PROTO_X25;
> -		return 0; /* return protocol only, no settable parameters */
> +		if (ifr->ifr_settings.size < size) {
> +			ifr->ifr_settings.size = size; /* data size wanted */
> +			return -ENOBUFS;
> +		}
> +		if (copy_to_user(x25_s, &state(hdlc)->settings, size))
> +			return -EFAULT;
> +		return 0;
>  
>  	case IF_PROTO_X25:
>  		if (!capable(CAP_NET_ADMIN))
> @@ -203,12 +243,35 @@ static int x25_ioctl(struct net_device *dev, struct ifreq *ifr)
>  		if (dev->flags & IFF_UP)
>  			return -EBUSY;
>  
> +		if (copy_from_user(&new_settings, x25_s, size))
> +			return -EFAULT;
> +
> +		if ((new_settings.dce != 0 &&
> +		     new_settings.dce != 1) ||
> +		    (new_settings.modulo != 8 &&
> +		     new_settings.modulo != 128) ||
> +		    new_settings.window < 1 ||
> +		    (new_settings.modulo == 8 &&
> +		     new_settings.window > 7) ||
> +		    (new_settings.modulo == 128 &&
> +		     new_settings.window > 127) ||
> +		    new_settings.t1 < 1 ||
> +		    new_settings.t1 > 255 ||
> +		    new_settings.t2 < 1 ||
> +		    new_settings.t2 > 255 ||
> +		    new_settings.n2 < 1 ||
> +		    new_settings.n2 > 255)
> +			return -EINVAL;
> +
>  		result=hdlc->attach(dev, ENCODING_NRZ,PARITY_CRC16_PR1_CCITT);
>  		if (result)
>  			return result;
>  
> -		if ((result = attach_hdlc_protocol(dev, &proto, 0)))
> +		if ((result = attach_hdlc_protocol(dev, &proto,
> +						   sizeof(struct x25_state))))
>  			return result;
> +
> +		memcpy(&state(hdlc)->settings, &new_settings, size);
>  		dev->type = ARPHRD_X25;
>  		call_netdevice_notifiers(NETDEV_POST_TYPE_CHANGE, dev);
>  		netif_dormant_off(dev);
> diff --git a/include/uapi/linux/hdlc/ioctl.h b/include/uapi/linux/hdlc/ioctl.h
> index 0fe4238e8246..3656ce8b8af0 100644
> --- a/include/uapi/linux/hdlc/ioctl.h
> +++ b/include/uapi/linux/hdlc/ioctl.h
> @@ -3,7 +3,7 @@
>  #define __HDLC_IOCTL_H__
>  
>  
> -#define GENERIC_HDLC_VERSION 4	/* For synchronization with sethdlc utility */
> +#define GENERIC_HDLC_VERSION 5	/* For synchronization with sethdlc utility */

What's the backward compatibility story in this code?

The IOCTL handling at least looks like it may start returning errors
to existing user space which could have expected the parameters to
IF_PROTO_X25 (other than just ifr_settings.type) to be ignored.

>  #define CLOCK_DEFAULT   0	/* Default setting */
>  #define CLOCK_EXT	1	/* External TX and RX clock - DTE */